The present invention relates to thrust augmentors for gas turbine engines and, more particularly, to heat shield designs for the fuel pipes of such thrust augmentors.
A typical jet aircraft engine configuration is shown schematically in FIG. 1A and is referred to generally as 11, with an engine axis 17. Engine 11 includes a turbine engine section 31 generally defined by arrows A, and a thrust augmentor 12 generally defined by arrows B. The gas flow path through the engine is represented by arrows C.
In order to increase the thrust temporarily of a gas turbine engine, a thrust augmentor is used. Such thrust augmentors are located downstream of the core engine and include a substantially cylindrical diffuser wall which defines the augmentor or afterburner channel, and a plurality of fuel tubes 33 projecting radially inwardly toward the axis 17, into the augmentor channel for injecting fuel into the hot exhaust gases of the core engine.
Examples of such thrust augmentors are disclosed in Nash et al., U.S. Pat. No. 4,901,527 and Gastebois et al., U.S. Pat. No. 4,899,539. Nash et al. discloses a thrust augmentor including fuel injectors extending radially inwardly through an outer casing and diffuser wall into the augmentor channel. Fairings surround the injectors, shielding the fuel pipes from heat from the hot core gas flow and downstream flame in the augmentor, and include an opening for directing cooling air from the bypass channel through the fairing to further protect the fuel pipes from the surrounding heat of the augmentor. Gastebois et al. discloses a thrust augmentor having a plurality of tubular injectors concentric with an outer sleeve which directs cooling air trapped by an air scoop in the bypass air duct, along the length of the fuel tube, thus also acting as a heat shield. The fuel tube is within a V-shaped flame stabilizer which opens downstream of the fuel tube. The fuel tube includes a plurality of orifices arranged along its length and which open in an upstream direction, so that fuel issues in counterflow fashion of the flame stabilizer.
A disadvantage with such designs is that it is often difficult to replace damaged heat shields. Disconnecting such heat shields from the supporting structure for replacement typically requires removal of the engine from an aircraft to gain access to attachment means from outside the augmentor channel. Consequently, aircraft availability is affected and engine downtime is increased. Accordingly, there is a need for a thrust augmentor heat shield which can be accessed from within the thrust augmentor channel and replaced without requiring access outside the outer wall of the channel.